1. Field of the Invention
The present invention generally relates to laminated wafers and to methods of making laminated wafers. The invention particularly relates to laminated wafers that provide added functions to optical elements. The invention more particularly relates to laminated functional wafers which are incorporated into optical elements using insert injection molding and to methods of making such laminated functional wafers.
2. Description of the Related Art
Plastic ophthalmic lenses made from materials such as polycarbonate and CR-39, have become popular due to their low cost and light weight over glass lenses. Polycarbonate lenses have superior impact resistance compared to CR-39 lenses, and are preferred for applications that require additional safety features. The use of polycarbonate lenses, has particularly become widespread in the United States. Consequently, the demand for sport goggles and sunglasses which are impact resistant has increased.
Typically, functional properties other than optical power are incorporated into polycarbonate lenses. For example, lenses with light polarization function are used to effectively cut glare from road and water surfaces. Photochromic properties may also be incorporated into a plastic lens, as well as color enhancement, color selection, mirror, tint, decoration, and indicia, to name a few.
U.S. Pat. Nos. 5,751,481 and 5,805,336 discloses techniques for incorporating light polarization function into a plastic lens. In this process, a polarized laminate is formed by adhering a polarizing film between two transparent polymeric sheets. The polarizing film is typically a stretched PVA film with absorbed iodine. The laminate is compression-formed under heat into a pre-curved lens blank. The transparent polymeric sheet on the concave side is substantially thicker than the polymeric sheet on the convex side. The polymeric sheet on the concave side is thick enough to allow the polarized lens blank to be surfaced into an ophthalmic polarized lens.
A more efficient and effective method to incorporate light polarization function into a lens manufactured from a thermoplastic material such as polycarbonate is insert injection molding. For example, U.S. Pat. No. 6,328,446 and 5,856,860, herein incorporated by reference, describes an insert injection molding method to manufacture polarized polycarbonate lenses. In this process, a polarizing plate wafer is first placed inside a mold cavity. Polycarbonate lens material is then injected into the cavity and fused to the back of the polarizing plate. The polarizing plate is a laminate consisting of a polarizing film with two protective transparent resin sheets bonded to each side of the polarizing film. The finished product is an injection molded, polarized polycarbonate lens.
Photochromic plastic lenses have been the subject of considerable attention due to the weight advantage and impact resistance they offer over glass lenses. Currently, several existing methods exists to incorporate photochromic properties into plastic lenses.
One method involves applying a coating to the lens surface containing dissolved photochromic compounds. For example, Japanese Patent Application 3-269507 discloses the process of applying a thermoset polyurethane coating containing photochromic compounds to the surface of a lens. U.S. Pat. No. 6,150,430 discloses a similar photochromic polyurethane coating applied to the surface of a lenses.
Another method involves coating a lens with a base coating, then imbibing a solution containing photochromic compounds into the base coating material. The most commonly used base material is polyurethane.
However, the two methods described above have significant shortcomings, especially when the photochromic lens has segmented power portions, e.g., a flat-top bifocal lens. Typically a coating of about 25 μm or more is needed to incorporate a sufficient quantity of photochromic compounds into the-base in order to provide the desired light blocking quality when the compounds are activated. This relatively thick coating is not suited for application on the surface of a segmented, multi-focal lens. An unacceptable segment line and coating thickness nonuniformity around the segment line are just a few of the major drawbacks of the technique.
Similar to polarized polycarbonate lenses, photochromic polycarbonate lenses can also be effectively produced with an insert injection molding method as disclosed in U.S. Pat. No. 6,328,446. In this process, a unitary photochromic laminate is first placed inside a mold cavity. Polycarbonate lens material is then injected into the cavity and fused to the back of the photochromic laminate, producing a photochromic polycarbonate lens. Because a thin photochromic layer in the laminate provides the photochromic functionality, a lens with any surface curvature is practical using the insert injection molding method.
Transparent resin laminates with light polarization function and transparent resin laminates with photochromic function have been disclosed in many patents and publications. For example, U.S. Pat. Nos. 4,427,741, 4,592,623, 4,774,141, 4,803,014, 5,051,309 and 6,055,096, incorporated herein by reference. Example photochromic laminates are disclosed in U.S. Pat. No. 4,889,413, U.S. Patent Publication No. 2002/01 97484, and WO 02/093235, all of which are incorporated by reference. Other photochromic laminates are disclosed in Japanese Patent Applications 61-276882, 63-178193, 4-358145, and 9-001 71 6.
The most commonly used structure for either a polarizing plate or a photochromic laminate is a functional layer bonded between two transparent resin sheets. The functional layer is often a polarizing film or a photochromic film. In this process, wafers (i.e., unitary laminates or plate) are cut from a large laminate or plate. The wafers serve as inserts in the insert injection molding process. FIG. 1 shows the cross section of a conventional wafer comprising a front transparent resin sheet 10, a back transparent resin sheet 20, and a functional layer 30. There may also exist adhesive layers (not shown) between the functional layer 30 and the transparent resin sheets 10 and 20.
One of the problems associated with conventional wafers in the manufacture of polarized or photochromic lenses by insert injection molding is the bleeding of the adhesive material and/or the functional layer material. By the term “bleeding” it is meant that the materials between the transparent resin sheets runs out of the cover of the resin sheets in the lateral direction. Often bleeding occurs from the deformation of the photochromic layer under the high temperature and pressure used during the molding process. In particular, bleeding occurs when the host material for the photochromic compounds melts and escapes from its position between the two transparent resin sheets of the laminate during the injection molding process.
The inventors have discovered that bleeding most frequently results from an excess amount of adhesive or host material and from using a material that is relatively too soft. Material bleeding will result in tooling contamination and increase the surface defect level of the molded lenses. Even more seriously, the bleedings can contaminate the coating solution which is often applied in a hard-coating application after the lens has been molded. This increases the coating defect level of the coated lenses.
Therefore, the need exists to overcome the bleeding problem associated with existing laminate wafers and methods of making these wafers. In particular, a need exists to reproducibly manufacture functional, lenses using the insert injection molding process that produces a lens without host material or adhesive bleeding.